Back-up pads for sheets of coated abrasive are well known in the art and are used in a variety of sanding, grinding and polishing operations such as auto body repair and refinishing, woodworking, and metalworking. As used herein, the phrase "coated abrasive" means an article having a backing and a plurality of abrasive grains bonded thereto. The abrasive grains may include grains adapted for polishing or buffing a workpiece. Examples of back-up pads and abrasive sheets are disclosed in U.S. Pat. Nos. 2,991,596; 3,082,582; 3,875,703 and 3,924,362 the entire contents of which are herein incorporated by reference.
As used herein the phrase "back-up pad" means an article generally comprising a resiliently compressible portion (e.g. constructed from an elastomer or foam such as polyurethane foam) having a front surface (e.g. circular) and a rear surface (e.g. circular). For example, some back-up pads include attachment means adjacent the rear surface which may comprise a recessed or post screw portion for attaching the back-up pad to a rotative source of power such as a random orbital sander (e.g. the sander disclosed in Bischof et al. U.S. Pat. No. 5,040,340 the entire contents of which are herein incorporated by reference), a hand or manually driven tool (e.g. the hand driven tool described in U.S. Pat. No. 2,794,303 the entire contents of which are herein incorporated by reference) or a dual action (DA) type sander. Back-up pads are generally available from the Minnesota Mining and Manufacturing Co. of St. Paul, Minn. under the trade names Hookit.TM. and Stikit.TM..
An abrasive (e.g. the abrasive discs described in U.S. Pat. Nos. 3,849,949 and 3,912,142 the entire contents of which are herein incorporated by reference) may be attached to the front surface of the back-up pad by a variety of attachment means. In U.S. Pat. No. 2,286,208 (the entire contents also incorporated by reference), a coated abrasive sheet is attached to a back-up pad by a coating of pressure sensitive adhesive. Another approach is to have loops that project from the abrasive sheet (as described in U.S. Pat. No. 4,609,581 herein incorporated by reference) and hooks that project from the front surface of the back-up pad. Yet another approach is to use the magnetic attachment described in Barton U.S. Pat. No. 4,667,447, the entire contents of which are also herein incorporated by reference.
During storage, transportation and display of back-up pads, it is important to protect the back-up pads, particularly the resilient portion of a back-up pad. A torn, punctured, dented, split, cracked, ripped or otherwise deformed resilient portion may mar or cause a deep, damaging scratch in a workpiece.
Back-up pads which include an attachment means comprising a male screw portion tend to be particularly susceptible to damage from, for example, the male screw portion of one pad damaging the front surface of another back-up pad. Damage to the front surface of a back-up pad may lead to a variety of undesirable results such as, for example, damage to the means for attaching an abrasive to the back-up pad, and a loss of pad weight balance resulting in rotational instability in a back-up pad used in conjunction a with rotative source of power.
FIG. 1 illustrates a portion of a packaging system typically used to enclose and protect a back-up pad. That system utilizes an opaque, relatively durable paper or chipboard sleeve 2 to wrap the resilient portion of the back-up pad. Indicia may be printed on the sleeve 2. Each pad is individually wrapped, and then a plurality of the wrapped back-up pads are typically placed or stacked in a box for subsequent transportation or storage.
The prior art packaging system shown in FIG. 1 suffers from many drawbacks including expense. Further, in order to view the back-up pad, the paper or cardboard sleeve 2 has to be removed. Additionally, as each wrapped pad is removed from the box used in the prior art system, the remaining pads tend to become haphazardly arranged in the box which (1) does not provide a desirable presentation of the product for sellers, vendors or other users, and (2) may result in damage to the remaining back-up pads.
Other packaging systems comprise a box having alternating layers of back-up pads and sheets of corrugated board. Again, such systems suffer from many drawbacks including expense and lack of visibility of the back-up pads.